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Leprosy (Hansen's Disease)

Research on Leprosy

NIAID has been supporting leprosy research around the world for many years. With the Mycobacterium leprae genome now identified, researchers are looking at several different approaches to combating leprosy.

Innovative research efforts are addressing such issues as transmission and the true extent of leprosy incidence. Studies are focusing on the areas of early detection (prior to developing clinical symptoms), prevention of nerve damage, surveillance of areas where drug resistance is occurring, and molecular epidemiology.

Tools for Researchers

Molecular tools have helped overcome challenges posed by the slow growth of M. leprae in vivo and its inability to grow in vitro. Other than humans, armadillos are the only animal known to be susceptible to leprosy. Because of this, colonies of armadillos have been important in research to model the disease. Since 1978, NIAID has supported contracts for the propagation of M. leprae in armadillos to derive sizable quantities of the bacterium, its DNA, and antigens as resources for researchers working throughout the world. The armadillo facility is located at the National Hansen’s Disease Program Laboratories (NHDP) in Baton Rouge, Louisiana, and the M. leprae research reagents are being developed at Colorado State University, Fort Collins.

As part of these NIAID-funded contracts, investigators at NHDP are developing the armadillo as a research animal model for human leprosy and investigators at Colorado State University are developing improved skin test antigens to detect leprosy. Trials to determine the safety of new skin test antigens were conducted in volunteers in the United States and at the Anandaban Hospital in Nepal to determine the utility of a skin test for epidemiologic surveillance and diagnosis in leprosy-endemic regions.

Transmission Discovery

NIAID-funded scientists at NHDP are also using genomic knowledge of M. leprae to examine leprosy transmission. From earlier epidemiological studies, NIAID-funded scientists at NHDP knew that M. leprae had been found among wild armadillos in Texas and Louisiana, suggesting that human contact with infected armadillos might lead to infection. Recently, the research team, led by by Richard W. Truman, Ph.D., compared the gene sequences of M. leprae samples taken from humans and infected wild armadillos and found that 64 percent of human samples had a particular genotype that had never been seen before. What’s more, 85 percent of armadillo samples shared that same genotype.

These results showed that the two strains were related and that wild armadillos were a likely source of some human infections. But more importantly, it established leprosy as a zoonosis: an infectious disease that can be transmitted back and forth between animals and humans.

Next Steps

Priorities for research in leprosy today include genetic probes for molecular epidemiology, and new immunologic tests for early detection of leprosy before nerve damage occurs. The goals are to provide evidence on routes of transmission and incubation periods and to develop new tools to prevent and, ultimately, eradicate leprosy.